Studies are planned to identify cellular activities which effect immunoregulation of cell- and antibody-mediated immune responses in mice infected with Trypanosoma cruzi. Emphasis will be placed on examining suppressor macrophages and a serum suppressor substance of experimental Chagas' disease on development of both anti-T. cruzi immune responses against heterologous antigens. Attempts will be made to block or abrogate suppression and, thereby, access its significance on immunity to the parasite.